As the temperatures kept plummeting, Delhi once again woke up to chills this morning, engulfed in thick clouds of smog and bringing down visibility to a minimum.
The IMD declares a cold wave in the plains if the minimum temperature dips to 4 degrees Celsius, and also when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than normal.
According to the IMD, a "cold day" is when the minimum temperature is less than 10 degrees Celsius and the maximum is at least 4.5 degrees Celsius below normal.
A "severe" cold day is when the maximum temperature is at least 6.5 notches below normal.
The IMD declares a cold wave in the plains if the minimum temperature dips to 4 degrees Celsius, and also when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than normal.
A few places in the capital also reported a cold day on Sunday— when the minimum temperature is less than or equal to 10 degrees Celsius and the maximum temperature is at least 4.5 degrees Celsius below normal. Delhi's primary weather station, Safdarjung observatory, recorded a minimum temperature of 5.3 degrees Celsius -- three notches below normal, and the maximum temperature settled at 16.2 degrees Celsius, five notches below normal and the lowest so far this season.
Moreover, a ‘severe’ cold wave is when the minimum temperature dips to two degrees Celsius or the departure from normal is more than 6.4 degrees Celsius.
What causes the cold wave?
“The winds were west-northwesterly but now they are north-northwesterly, blowing at about 10kmph over Delhi. A layer of upper haze when morning fog hasn’t lifted completely and is also obscuring sunshine during the day giving a feel of biting cold. These conditions will last for a day before temperatures rise gradually," Mahesh Palawat, vice president, climate and meteorology, at Skymet Weather, was quoted saying by several media reports.
A cold wave can result from cloud cover, or more precisely, from a lack of cloud cover. A decrease in cloud cover causes more heat to escape from the Earth's surface, resulting in a cooler surface and lower temperatures because clouds absorb infrared radiation from the planet.